Don't install letsencrypt certificates if we operate behind a proxy

tasks/main.yml

@@ -12,7 +12,7 @@
       - domains
     when: item.1.protocol|default("https") == "https" and item.1.letsencrypt|default(true)
 
-  when: '"letsencrypt" not in excluded_roles'
+  when: '"letsencrypt" not in excluded_roles and groups.proxyserver is not defined'
 
 - block:
   - name: "Install Drupal"